In the case of internal combustion engines with a high power density, particular measures are necessary for cooling the pistons.
It is known in this connection to act upon the piston with cooling splash oil via splash nozzles arranged in the crank space of the internal combustion engine.
DE 25 39 470 A1 shows a piston of this type with an associated spray nozzle, wherein the ejected splash oil is splashed into the downwardly open piston interior, and therefore the lower side of the piston head, which side faces the piston interior, is constantly cooled. However, it is demonstrated in DE 25 39 470 A1 that splash cooling of this type is inadequate in the event of a higher power density of the engine. It is therefore proposed in DE 25 39 470 A1, at the lower end of the piston remote from the combustion chamber, to arrange an oil-connecting trough which annularly surrounds the connecting-rod passage, collects at least a portion of the oil splashed against the lower side of the piston head and, over the course of the movements of the piston, acts as a shaker space and holds the collected oil against the piston head again.
Although the cooling of the piston is therefore improved, a further intensification of the cooling nevertheless remains desirable. In particular, there is the difficulty in an arrangement as per DE 25 39 470 A1 that the splash jet of the splash nozzle arranged outside the movement space of the connecting rod first of all impinges against an eccentric region of the piston head, and therefore the piston head is inevitably cooled non-uniformly.
DE 10 2008 055 911 A1 shows pistons which are highly loadable thermally and have an outer annular cooling duct in the vicinity of the fire land forming the combustion-chamber-side edge of the piston head and in the vicinity of the piston ring portion of the piston. Cooling oil can be sprayed into said outer cooling duct in order effectively to cool the thermally extremely highly loaded fire land and the piston ring portion. In order to empty the cooling duct, radial ducts are provided on the inner circumference of the latter, via which radial ducts the annular outer cooling duct communicates with a cavity arranged below the central region of the piston head. Said cavity acts in the manner of a shaker space, and therefore, during the reciprocating movements of the piston, the oil accommodated in the cavity is continuously thrown against the lower side of the piston head. The oil is ejected from the cavity through openings in the direction of the articulated connection between piston and connecting rod, and therefore an intensive lubrication of said joint can additionally be ensured.
Similar pistons are depicted in DE 10 2009 032 916 A1 and DE 10 2009 032 865 A1.
However, it has to be accepted in the case of pistons of this type that the oil serving for cooling the piston head has previously already absorbed large amounts of heat within the outer cooling duct and has accordingly reached a comparatively high temperature.